Field of the Invention
The present invention relates to electric scissors, used to prune branches of trees or the like, for cutting objects to be cut, such as the branches, by opening and closing the blades using a drive power of a motor.
Background Art
Conventionally, branches or the like have been pruned with scissors by opening/closing blades of scissors with a hand of the user. However, for the purpose of saving labor of this work, electric scissors are proposed that can cut objects to be cut, such as the branches, by opening/closing the blades using a drive power of a motor.
Such electric scissors include a fixed blade and a movable blade being rotatable around a shaft serving as a fulcrum. A configuration referred to as a link type and a configuration referred to as a gear type are known as the configurations of systems for driving the movable blade.
Link-type electric scissors are configured so that the movable blade thereof is formed into an L-shape, for example, having a cutting edge portion on one side of the movable blade with respect to the shaft on which the movable blade is supported and having an arm portion on the other side of the movable blade. Furthermore, the electric scissors have a ball screw for converting a rotation of a motor into a linear motion of a nut portion and a link for connecting the nut portion to the arm portion of the movable blade. With this configuration, the linear movement of the nut portion is transmitted to the arm portion of the movable blade via the link, and the movable blade is rotated around the shaft serving as a fulcrum (for example, refer to Patent Document 1).
Patent Document 1: U.S. Pat. No. 5,002,135
Gear-type electric scissors are configured so that the movable blade thereof has an arc-shaped gear disposed coaxially with a shaft on which the movable blade is supported and so that the rotation of a motor is transmitted to the movable blade using a mechanism in which a bevel gear and a spur gear or the like are combined (for example, refer to Patent Document 2).
Patent Document 2: JP-A-11-128561
The link-type electric scissors are characterized in that as the blades are closed, the cutting torque thereof becomes low. Generally speaking, in the case of cutting an object to be cut with scissors, a large torque is not required at the beginning of the closing of the blades. However, a large torque is required as the blades are closed.
For this reason, for the purpose of obtaining a desired torque when the blades are closed, the link-type electric scissors are configured so that a large torque can be generated using a motor having a large output, for example. With this configuration, the large torque is applied at the beginning of the closing of the blades.
Hence, a load applied to the drive system, such as the ball screw mechanism, becomes large, and the durability of the drive system is degraded. On the other hand, for the purpose of improving the durability, the drive system is required to be constructed sturdily so as to cope with the large load. Consequently, although the electric scissors are used as a tool held in the hand, it is difficult to make the electric scissors light in weight, and the apparatus eventually becomes large in size and the operability thereof is degraded.
In the gear-type electric scissors, a constant torque is obtained regardless of the opening degree of the blades. However, the gears thereof are required to be increased in thickness to withstand the large load. It is thus difficult to make the electric scissors light in weight, and the apparatus eventually becomes large in size. On the other hand, if the gears are decreased in thickness to make the apparatus compact in size and light in weight, the durability thereof is degraded.